Surface modified unit cell lattice structures for optimized secure freeform fabrication

ABSTRACT

Aspects of the present disclosure relate generally to preparing models of three-dimensional structures. In particular, a model of a three-dimensional structure constructed of porous geometries is prepared. A component file including a porous CAD volume having a boundary is prepared. A space including the porous CAD volume is populated with unit cells. The unit cells are populated with porous geometries having a plurality of struts having nodes on each end. The space is populated with at least one elongated fixation element extending beyond the boundary to produce an interlocking feature enabling assembly or engagement with a mating structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patent application Ser. No. 13/441,154, filed Apr. 6, 2012, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to preparing computer-generated models of porous structures. In particular, the surfaces of computer-generated models of structures may be modified through movement and removal of struts and nodes of porous geometries near the surface to produce surfaces conforming to the surfaces of intended physical structures being modeled.

BACKGROUND OF THE INVENTION

The field of free-form fabrication has seen many important recent advances in the fabrication of articles directly from computer controlled databases. These advances, many of which are in the field of rapid prototyping of articles such as prototype parts and mold dies, have greatly reduced the time and expense required to fabricate articles, particularly in contrast to conventional machining processes in which a block of material, such as a metal, is machined according to engineering drawings.

One example of a modern rapid prototyping technology is a selective laser sintering process. According to this technology, articles are produced in layer-wise fashion from a laser-fusible powder that is dispensed one layer at a time. The powder is sintered, by the application of laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross section of the article. After the sintering of the powder on one particular layer, an additional layer of powder is dispensed, and the process repeated, with sintering taking place between the current layer and the previously laid layers until the article is complete. Detailed descriptions of the selective laser sintering technology may be found in U.S. Pats. No. 4,863,538, 5,017,753, 5,076,869 and 4,944,817, the entire disclosures of which are incorporated by reference herein. Similarly, a detailed description of the use of selective laser melting technology may be found in U.S. patent application Ser. No. 10/704,270, filed on Nov. 7, 2003, now U.S. Pat. No. 7,537,664 (“the '664 Patent”), the disclosure of which is incorporated by reference herein. The selective laser melting and sintering technologies have enabled the direct manufacture of solid or porous three-dimensional articles of high resolution and dimensional accuracy from a variety of materials including wax, metal powders with binders, polycarbonate, nylon, other plastics and composite materials, such as polymer-coated metals and ceramics.

The invention claimed in the '664 Patent was the first of many inventions assigned to Howmedica Osteonics Corporation, who has been a pioneer in porous surface and porous structure formation, specifically for use in orthopedics. For instance, other applications in this area, such as U.S. patent application Ser. No. 11/027,421 filed on Dec. 30, 2004 (“the '421 Application”), and U.S. patent application Ser. No. 12/846,327 filed on Jul. 29, 2010 (“the '327 Application”), the entire disclosures of which are hereby incorporated by reference herein, have taught the generation of a population of porous geometry, a mathematical representation of the portion of geometry of the porous structure to be built within a region defined by predetermined unit cells or imaginary volumes that are organized to fill and form a predetermined build geometry, or model build structure, which may be used to produce a near net-shape of an intended porous tissue in-growth structure. The predetermined build geometry, or overall computer-aided design (CAD) geometry, may refer to the mathematical or pictorial representation (such as that on a computer display) of the extent or outer boundary of an intended physical structure to be manufactured. In the case of physical components that include both porous material and solid material, the model build structure may be an assembly of solid and porous CAD volumes that model the outer boundaries of the respective solid and porous materials intended to be manufactured. Furthermore, these applications teach the randomization of the position of interconnected nodes, or points of intersection between two struts or between a strut and a substrate, that define each of the porous geometries while maintaining the interconnectivity between the nodes. As previously taught, such randomization may accomplished by changing the coordinate positions of the nodes in the x, y, and z directions of a Cartesian coordinate system, to new positions based on a defined mathematical function. To achieve a required external shape for a device being created, these references have taught the truncation or removal of struts forming the unit cells at the outer surface. Such truncation helps to achieve the near-net shape of the intended structure, but truncated or clipped struts may, in some instances, create a situation where the porous geometries are un-supported by the underlying structures. These truncated struts may present a potential site for the generation of debris as protruding struts may fracture.

Additionally, although modeling structures with porous geometries has become a very useful tool in modern rapid prototyping, models of a porous ingrowth structure may in some instances include a surface that generates an intended structure that, prior to bone ingrowth into the structure, leaves a gap between the porous ingrowth structure and resected bone or other bone structure with which the porous ingrowth structure interfaces. While bone cement may be used at the time of surgery to provide initial stability, the application of such requires additional steps, risks, and time, and may interfere with the intended bone ingrowth capabilities of the surface. Moreover, the mechanical integrity of the cement mantle is dependent upon surgical technique as well as the cement material. Over a long period of time, the cement acts as an additional mechanical structure but adds additional risks due to potential failure within the cement mantle and at both the cement-bone and cement-implant interfaces.

Thus, a new method is needed to create build geometries having surfaces that are more robust and less likely to form debris as well as that provide initial stability that eliminates the need for cement and reduces or eliminates these risks.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a process of preparing a computer generated model of a three dimensional structure constructed of porous geometries may include a step of preparing a computer-generated component file including a porous CAD volume having a boundary having a predefined portion. The process for preparing the model may include a step of populating, by a processor, a space. The space may include the porous CAD volume which may be populated by unit cells that overlap the predefined portion of the boundary. The process for preparing the model may include a step of populating, by a processor, the unit cells with porous geometries. The porous geometries may have a plurality of struts with nodes at each of the ends of the struts including a first strut overlapping the predefined portion of the boundary. The first strut may have a length, a first node outside the porous CAD volume, and a second node inside the porous CAD volume. The process for preparing the model may include a step of removing all struts entirely outside the porous CAD volume in which after the removal of the struts entirely outside the porous CAD volume, each of the remaining struts is connected to a node at each end of the remaining struts.

In accordance with a further embodiment of the invention, a process of preparing a computer generated model of a three dimensional structure constructed of porous geometries may include a step of preparing a computer-generated component file including a porous CAD volume having a boundary with a predefined portion. The process may include a step of populating, by a processor, a space. The space may include the porous CAD volume which may be populated by unit cells that overlap the predefined portion of the boundary. The process for preparing the model may include a step of populating, by a processor, the unit cells with porous geometries in which the porous geometries have a plurality of struts with nodes at each of the ends of the struts including a first strut that intersects the predefined portion of the boundary. The first strut may have a length and a first node at a first location that may be on the predefined outer boundary or outside the porous CAD volume. The process for preparing the model may include a step of removing all struts entirely outside the porous CAD volume. The process for preparing the model may include a step of moving the first node from the first location to a second location.

In accordance with a further embodiment of the invention, a tangible computer-readable storage medium may have computer readable instructions of a program stored on the medium. The instructions, when executed by a processor, may cause the processor to perform a process of preparing a computer generated model of a three dimensional structure constructed of unit cells. The process of preparing the model may include a step of preparing a computer-generated component file including a porous CAD volume having a boundary having a predefined portion. The process for preparing the model may include a step of populating, by a processor, a space. The space may include the porous CAD volume which may be populated by unit cells that overlap the predefined portion of the boundary. The process for preparing the model may include a step of populating, by a processor, the unit cells with porous geometries. The porous geometries may have a plurality of struts with nodes at each of the ends of the struts including a first strut overlapping the predefined portion of the boundary. The first strut may have a length, a first node outside the porous CAD volume, and a second node inside the porous CAD volume. The process for preparing the model may include a step of removing all struts entirely outside the porous CAD volume in which after the removal of the struts entirely outside the porous CAD volume, each of the remaining struts is connected to a node at each end of the remaining struts.

In accordance with a further embodiment of the invention, a process of preparing a computer-generated model of a three-dimensional structure constructed of porous geometries may include a step of preparing a computer-generated component file including a porous CAD volume having a boundary. The process for preparing the model may include a step of populating, by a processor, a space including the porous CAD volume with unit cells. The process for preparing the model may include a step of populating, by a processor, the unit cells with porous geometries. A plurality of the porous geometries may have a plurality of struts with nodes at each of the ends of the struts. The process for preparing the model may include a step of populating, by a processor, the space with at least one fixation element that may extend beyond the boundary to produce an interlocking feature. Such an interlocking feature may enable assembly or engagement with a mating structure.

In accordance with a further embodiment of the invention, a process of producing a three-dimensional structure may include a step of preparing a computer-generated model of a three-dimensional structure such as in the manner just described. The process of producing the structure may include a step of depositing a metal powder onto a substrate. The process of producing the structure may include a step of scanning a beam onto the deposited metal powder to form a first physical layer of a porous section. The first physical layer may correspond to a portion of a porous CAD volume of the model of the three-dimensional structure. The three-dimensional structure may have a geometric lattice structure constructed of porous geometries and a boundary. The porous geometries may be formed by a plurality of struts. Each of the plurality of struts may have a node on each end of the strut. The process of producing the structure may include a step of repeating the step of depositing the metal powder onto the substrate. The process of producing the structure may include a step of repeating the step of scanning the beam onto the deposited metal powder to form additional physical layers of the three-dimensional structure. The process may include a step of forming an elongated fixation member for assembly or engagement with a mating structure. The fixation member may correspond to the elongated fixation element and may extend beyond the boundary.

In accordance with a further embodiment of the invention, a tangible computer-readable storage medium may have computer readable instructions of a program stored on the medium. The instructions, when executed by a processor, may cause the processor to perform a process of preparing a computer-generated model of a three-dimensional structure constructed of unit cells. The process of preparing the model may include a step of preparing a computer-generated component file including a porous CAD volume having a boundary. The process for preparing the model may include a step of populating, by a processor, a space including the porous CAD volume with unit cells. The process for preparing the model may include a step of populating, by a processor, the unit cells with porous geometries. A plurality of the porous geometries may have a plurality of struts with nodes at each of the ends of the struts. The process for preparing the model may include a step of populating, by a processor, the space with at least one fixation element that may extend beyond the boundary to produce an interlocking feature. Such an interlocking feature may enable assembly or engagement with a mating structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram of a system in accordance with an exemplary embodiment of the present invention;

FIG. 2( a) is a three-dimensional schematic representation of two unit cells and two porous geometries located therein;

FIG. 2( b) is a three-dimensional schematic representation of a spatial arrangement of melt spots that may be used to create the porous geometries of FIG. 2 a;

FIG. 3 illustrates a two-dimensional representation of a bounding box containing unit cells in accordance with an embodiment of the invention;

FIG. 4 illustrates the unit cells of FIG. 3 separated into those that intersect a boundary of a porous CAD volume and those that do not intersect the porous CAD volume

FIG. 5 shows the complete unit cells lying within the boundary of the porous CAD volume that are retained as shown in FIG. 4;

FIG. 6 illustrates a wireframe of porous geometries created within the retained unit cells shown in FIG. 5;

FIG. 7( a) illustrates a wireframe of porous geometries created within the unit cells that intersect the boundary of the porous CAD volume shown in FIG. 4;

FIG. 7( b) illustrates the nodes of the porous geometries within the unit cells of FIG. 7( a).

FIGS. 8( a) and (b) illustrate the wireframe of the porous geometries of FIG. 7 after clipping struts of the porous geometries at their intersections with the boundary of the porous CAD volume;

FIGS. 9( a) and (b) illustrate the wireframe of the porous geometries of FIG. 7 after clipping the full lengths of struts that overlap the boundary of the porous CAD volume;

FIGS. 10( a) and (b) illustrate the wireframe of the porous geometries of FIG. 7 after clipping the full lengths of struts that lie entirely outside the boundary of the porous CAD volume;

FIGS. 11( a) and (b) illustrate the wireframe of the porous geometries of FIG. 7 after clipping the full length of struts overlapping the boundary and having an inner node closest to the boundary to their respective inner nodes and the full length of struts lying entirely outside the boundary, while retaining the struts having the full length of struts overlapping the boundary and having an outer node closest to the boundary of the porous CAD volume;

FIGS. 12( a) and (b) illustrate the wireframe of the porous geometries of FIG. 11 after repositioning of the nodes closest to the boundary to positions along the boundary of the porous CAD volume through conformal manipulation;

FIGS. 13( a) and (b) show plan and side cross-sectional views, respectively, of a solid CAD volume surrounded by a boundary of a porous CAD volume of a tapered cylindrical geometry for use in accordance with an embodiment of the invention;

FIGS. 14( a) and (b) show plan and side cross-sectional views, respectively, of the tapered cylindrical geometry of FIG. 13, wherein nodes are populated at corners of unit cells within slices of the porous CAD volume through the use of polar coordinates;

FIGS. 15( a)-(c) show a plan view including unit cells, a plan view without unit cells, and a side cross-sectional view, respectively, of the tapered cylindrical geometry of FIG. 14, wherein struts connecting the nodes have been generated in a conformal manner;

FIGS. 16( a) and (b) illustrate plan cross-sectional views of the tapered cylindrical geometry of FIG. 15, before and after, respectively, repositioning of the nodes circumferentially about the cylindrical geometry at a boundary thereof in the same direction to create a structure with torque resistant properties.

FIG. 17 illustrates a plan cross-sectional view of the tapered cylindrical geometry of FIG. 16( a) after repositioning of the nodes circumferentially about the cylindrical geometry at the boundary thereof in opposite directions on opposite portions to create a structure with torque resistant properties;

FIGS. 18( a) and (b) illustrate side cross-sectional views of the tapered cylindrical geometry of FIG. 15, before and after, respectively, repositioning of the nodes longitudinally along the cylindrical geometry at the boundary thereof to create structures with anti back-out properties;

FIGS. 19( a)-(c) illustrate computer-generated models of cylindrical structures created by (a) clipping struts, positioned using Cartesian coordinates, at a boundary of a porous CAD volume, (b) positioning nodes based on polar coordinates, and (c) positioning nodes using Cartesian coordinates including repositioning of the nodes closest to the boundary to positions along the boundary of the porous CAD volume through conformal manipulation;

FIGS. 20( a)-(c) illustrate computer-generated models of structures created by positioning struts based on polar coordinates and then displacing nodes by varying amounts to create anti-back out functions;

FIG. 21 is a schematic of a surface produced by manipulating nodes in accordance with an embodiment of the invention to create a desired surface roughness;

FIGS. 22( a)-(c) illustrate a process of roughening a predetermined surface by moving nodes within a defined region along the surface in accordance with an embodiment of the invention;

FIGS. 23( a) and (b) show coupons having surfaces prepared by (a) applying and (b) not applying a predetermined surface roughness thereto in accordance with an embodiment of the present invention;

FIG. 24 shows a curved surface prepared by applying a predetermined surface roughness thereto in accordance with an embodiment of the present invention;

FIGS. 25( a) and (b) show examples of flat surfaces prepared by applying a predetermined surface roughness thereto to create surface labelling in accordance with an embodiment of the invention;

FIGS. 26( a) and (b) illustrate side elevation and plan views, respectively, of a model of a flat surface having surface node deformation to create irregularity in a specific area of a regular structure in accordance with an embodiment of the present invention;

FIG. 27 shows an example of a curved surface having surface node deformation to create irregularity in a specific area of a regular structure in accordance with an embodiment of the invention;

FIGS. 28( a) and (b) illustrate the wireframes of the porous geometries of FIGS. 12 and 15, respectively, having portions of struts added to the surface nodes of the respective porous CAD volumes;

FIG. 29 is a process flow diagram in accordance with an embodiment of the invention;

FIG. 30 is another process flow diagram in accordance with an embodiment of the invention;

FIG. 31 is another process flow diagram in accordance with an embodiment of the invention;

FIG. 32 is another process flow diagram in accordance with an embodiment of the invention;

FIGS. 33( a) and (b) illustrate elongated fixation elements extending from the wireframe of FIG. 12 in accordance with an embodiment of the invention;

FIGS. 34( a) and (b) illustrate elongated fixation elements extending from the wireframe of FIG. 12 in accordance with an embodiment of the invention;

FIGS. 35( a)-(c) show a plan view including unit cells, a plan view without unit cells, and a side cross-sectional view, respectively, of the tapered cylindrical geometry of FIG. 15, wherein elongated fixation elements extend from a substrate thereof;

FIG. 36 shows a cross-sectional view of a model build structure of a femoral knee implant having elongated fixation elements extending from a porous CAD volume thereof in accordance with an embodiment of the invention; and

FIGS. 37( a) and (b) show a portion of a model build structure of a tibial knee implant having elongated fixation elements extending from a solid CAD volume thereof and through a porous CAD volume thereof in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates generally to generating computer models of three-dimensional structures. These models may be used to prepare porous tissue in-growth structures in medical implants and prostheses. The models may include features corresponding to tangible structures having nodes along a predefined outer boundary.

FIG. 1 depicts a system 105 that may be used, among other functions, to generate, store and share three-dimensional models of structures. The system 105 may include at least one server computer 110, a first client computer 120, and in some instances, at least a second client computer 130. These computers may send and receive information via a network 140. For example, a first user may generate a model at the first client device 120. The model may then be uploaded to the server 110 and distributed via the network 140 to the second client computer 130 for viewing and modification by at least a second user.

The network 140, and intervening communication points, may comprise various configurations and protocols including the Internet, World Wide Web, intranets, virtual private networks, wide area networks, local networks, private networks using communication protocols proprietary to one or more companies, Ethernet, WiFi and HTTP, and various combinations of the foregoing. Such communication may be facilitated by any device capable of transmitting data to and from other computers, such as modems (e.g., dial-up, cable or fiber optic) and wireless interfaces. Although only a few devices are depicted in FIG. 1, a typical system may include a large number of connected computers, with each different computer being at a different communication point of the network.

Each of computers 110, 120, and 130 may include a processor and memory. For example, server 110 may include memory 114 which stores information accessible by a processor 112, computer 120 may include memory 124 which stores information accessible by a processor 122, and computer 130 may include memory 134 which stores information accessible by a processor 132.

The processors 112, 122, 132 may be any conventional processor, such as commercially available CPUs. Alternatively, the processors may be dedicated controllers such as an ASIC, FPGA, or other hardware-based processor. Although shown in FIG. 1 as being within the same block, the processor and memory may actually comprise multiple processors and memories that may or may not be stored within the same physical housing. For example, memories may be a hard drive or other storage media located in a server farm of a network data center. Accordingly, references to a processor, memory, or computer will be understood to include references to a collection of processors, memories, or computers that may or may not operate in parallel.

The memories may include a first part storing applications or instructions 116, 126, 136 that may be executed by the respective processor. The instructions 116, 126, 136 may be any set of instructions to be executed directly (such as machine code) or indirectly (such as scripts) by the processor. In that regard, the terms “applications,” “instructions,” “steps” and “programs” may be used interchangeably herein.

The memories may also include a second part storing data 118, 128, 138 that may be retrieved, stored or modified in accordance with the respective instructions. The memory may include any type capable of storing information accessible by the processor, such as a hard-drive, memory card, ROM, RAM, DVD, CD-ROM, write-capable, and read-only memories or various combinations of the foregoing, where the applications 116 and data 118 are stored on the same or different types of media.

In addition to a processor, memory and instructions, client computers 120, 130, 131, 133 may have all of the components used in connection with a personal computer. For example, the client computers may include an electronic display 150, 151 (e.g., a monitor having a screen, a touch-screen, a projector, a television, a computer printer or any other electrical device that is operable to display information), one or more user inputs 152, 153 (e.g., a mouse, keyboard, touch screen and/or microphone), speakers 154, 155, and all of the components used for connecting these elements to one another.

Instructions 126, 136 of the first and second client devices 120, 130 may include building applications 125, 135. For example, the building applications may be used by a user to create three-dimensional structures, such as those described further herein. The building applications may be associated with a graphical user interface for displaying on a client device in order to allow the user to utilize the functions of the building applications.

A building application may be a computer-aided design (CAD) three-dimensional (3-D) modeling program or equivalent as known in the art. Available CAD programs capable of generating such a structure include Autodesk® AutoCAD®, Creo® by Parametric Technology Corporation (formerly Pro/Engineer), Siemens PLM Software NX™ (formerly Unigraphics), and CATIA® by Dassault Systèmes. Such structures may be those described in the '421 Application.

The data 118, 128, 138 need not be limited by any particular data structure. For example, the data may be stored in computer registers, in a relational database as a table having a plurality of different fields and records, or XML documents. The data may also be formatted into any computer-readable format such as, but not limited to, binary values, ASCII or Unicode. Moreover, the data may comprise any information sufficient to identify the relevant information, such as numbers, descriptive text, proprietary codes, pointers, references to data stored in other memories (including other network locations) or information that is used by a function to calculate the relevant data. For example, the data 128 of the first client device 120 may include information used by the building application 125 to create three-dimensional models.

In addition to the operations described above and illustrated in the figuress, various other operations will now be described. It should be understood that the following operations do not have to be performed in the precise order described below. Rather, various steps may be handled in a different order or simultaneously. Steps may also be omitted or added unless otherwise stated herein.

An overall three-dimensional representation of a component may first be generated by preparing a CAD model. This overall CAD model may comprise of one or more distinct CAD volumes that are intended to be manufactured as either solid or porous geometries.

Solid CAD volumes can be sliced into layers of a predetermined thickness ready for hatching, re-merging with the porous volume (post-lattice generation) and subsequent manufacture.

Porous CAD volumes (the basic principles of which are detailed in FIGS. 2( a) and (b) can be processed using bespoke software. In this case the porous geometry is made up of a plurality of struts organized within tessellating unit cells 60. Many designs of porous geometry are possible to impart various strength, surface, and/or other characteristics into the porous CAD volume. For example, these porous geometries can be used to control the shape, type, degree, density, and size of porosity within the structure. Such porous geometry designs can be dodecahedral, octahedral, tetrahedral (diamond), as well as many other various shapes. In comparison, dodecahedral porous geometries have a different mechanical performance than a tetrahedral structure. Besides these regular geometric shapes, the porous geometries of the present invention may be configured to have irregular shapes where various sides and dimensions have little if any repeating sequences. Porous geometries can even be configured into constructs that closely mimic the structure of trabecular bone. Porous geometries can be space filling, in which all the space within a three-dimensional object is filled with porous geometries but do not always fill the space of an object they are used to produce.

FIG. 3 shows in greater detail a portion of a model build structure 50, generated through the use of an engineering design package such as that described previously herein.

The first step in creating a porous CAD volume is calculate a bounding box, i.e., a box whose x, y, and z dimensions correspond to, or are slightly larger than, a defined boundary of the porous CAD volume, which may be the entire boundary or a portion of a boundary as shown in FIG. 3. This bounding box is then divided into a number of unit cells defined by x, y, and z dimensions. Calculations are then performed during an interrogation on each individual unit cell to ascertain if each cell is within, or intersects the boundary of the porous CAD volume, as illustrated by FIGS. 4 and 5. If these conditions are satisfied for an individual cell, the cell is retained, whereas if they are not, the cell is discarded. Once all cells have been interrogated, porous geometry is populated within the cells that have been retained, as shown in FIGS. 6 and 7).

Various building blocks make up a porous geometry. Referring again to FIGS. 2 and 3 each of the porous geometries are made up of struts 65, or segments having a length. Nearly all of the struts 65 of the model build structure 50 meet at a node or intersection 70. The position of the nodes may be identified within an array of the data of the processor according to Cartesian, polar coordinates, or other user-defined coordinates.

The porous CAD volume has a predefined boundary 100 that corresponds to the intended outer surface of the part being designed. A portion of the boundary 100 is illustrated in FIG. 7. As shown, some of the unit cells 60 along the predefined boundary 100 have overlapping struts 8-21 that cross over the boundary 100. The struts 8-21 have inner nodes 26-29, 31, and 33 within the boundary 100 of the porous CAD volume and outer nodes 25, 30, 32, 34, and 35 outside of the boundary 100.

To produce a porous structure having struts that terminate along the boundary, the overlapping struts may be clipped such that any portion of the overlapping struts beyond the predefined boundary is removed. FIG. 8 depicts a model build structure 50 generated according to this clipping approach, in other words, after the overlapping struts 8-21 have been clipped. The overlapping struts 8-21 are now shorter. The ends of each of the overlapping struts 8-21 now lie along the predefined outer boundary 100 and none of the overlapping struts 8-21 extend past the boundary 100.

In some cases this clipping approach may be appropriate. However, the struts that have been shortened may not be supported at their outer points as can be seen in the model of FIG. 19( a), and as such they can act as cantilevers and may result in an increased risk of debris formation. In some instances (assuming a flat edge is present), the porous CAD volume may be modified so that the boundary lies along a whole number of unit cells. In this instance there is no need for the clipping operation. This mitigates the possibility of debris generation as the end of each strut is supported by at least one other strut, and is correspondingly less prone to failure.

FIG. 9 shows the model build structure 50 prepared by another approach where the full length of struts that overlap the surface of the porous CAD volume are removed to the inner node. Thus the overlapping struts 8-21 are removed. Preferably, removal of these struts leaves only the complete porous geometries. However, this approach may leave the surface rough, uneven and nonconforming to the original porous CAD volume as some of the unit cells 60 do not reach the outer boundary 100.

FIG. 10 shows the model build structure 50 prepared by another approach where the full length of struts that overlap the surface of the porous CAD volume are retained to their respective outer nodes. In this manner, the overlapping struts 8-21 remain beyond the boundary 100 of the porous CAD volume.

FIG. 11 shows the model build structure 50 prepared by yet a further approach where each of these struts 8-21 are either fully retained or fully removed, depending on the distance of their nodes from the boundary 100 of the porous CAD volume. In the example shown, each of the unit cells 60 outside the outer boundary 100 as well as the struts 9-12, 16 and 19 are removed (or marked for removal). The struts selected for removal are those overlapping struts in which the node outside the boundary, i.e., the outer node, is further from the boundary than the corresponding node of the overlapping strut inside the boundary, i.e., the inner node. In contrast, the overlapping struts 8, 13-15, 17-18, and 20-21 are not removed because their corresponding nodes 25, 30, 32, 34, and 35, although outside the outer boundary 100 are closer to the boundary 100 than their corresponding inner nodes.

FIG. 12 shows the model build structure 50 prepared after clipping, followed by the repositioning of the remaining nodes 25-35, closest to the boundary 100 of the porous CAD volume to coincide with the boundary 100. In some embodiments, each of the nodes 25-35 closest to the boundary 100 may be repositioned to a location determined by a mathematical calculation based on the original position of each of these nodes, e.g., the distance from the boundary of each of these nodes, or the original length of the struts attached to these nodes that overlap the boundary or both of these values. In this manner, the shape of the structure may be maintained when having nodes along the boundary.

As further shown in FIG. 12, when the nodes 25-35 are repositioned, the remaining struts connected to the nodes 25-35 may then be lengthened or shortened as required to maintain connectivity between the nodes. In this manner, the outermost nodes and struts may be positioned such that they do not coincide with the boundary by any function of the cell size or geometry. This effect can be seen clearly in FIG. 19( c).

In a variant of this embodiment, the nodes 25-35 may not be moved but instead discarded and replaced by new nodes. Additionally, the struts connected to the nodes 25-35 may be replaced by new struts that are longer or shorter than the original struts to maintain the connectivity between the nodes.

The use of polar or spherical coordinates to define nodes may be preferred to the use of Cartesian coordinates when a surface of a model build structure to be formed is curvate or cylindrical. In this manner, nodes repositioned on a boundary may be positioned at the same angle defining a replaced node but at a different radius from the origin of a polar coordinate system being used to create a model build structure. However, other user-defined coordinates may be used to create conformal structures. In other words, a user-defined node positioning system may be used to form a model build structure having nodes along an outer boundary that fit the contours of the outer boundary of the component being modeled.

FIG. 13 shows various cross sections of a tapered, cylindrical geometry. The gray color represents the solid CAD volume which is bounded by a clear, porous CAD volume.

FIG. 14 further shows the geometry of FIG. 13 subsequent to the generation of a plurality of outer nodes 410 and a plurality of inner nodes 430 along inner and outer boundaries 435, 445 of the porous CAD volume. Such nodes define the vertices of unit cells 450 which are created by virtually slicing the porous CAD volume according to the unit cell height. This operation produces polar rings that are then populated with volumes that pattern radially around the ring of the part. These volumes define the unit cells for the part.

FIG. 15 shows the population of the unit cells 450 created in the previous stage. The depicted geometry is based on the preferred octahedral cell as described previously herein but could be based on any porous geometry. These porous geometries are then defined by nodes with connecting struts or segments 480, all of which meet at the defined surface of the porous CAD volume 500. This effect can be seen clearly in FIG. 19( b).

Creation of beneficial surface properties can be achieved through the movement of the nodes 410 at the outer surface 500 of the porous CAD volume. FIGS. 16 and 17 detail the creation of torque or movement resisting features on the surface of cylindrical components. The nodes 410-427 that lie on the outermost boundary of the porous CAD volume 500 can be manipulated to be repositioned along the surface of the porous CAD volume 500 in either direction to create a deformed unit cell with a preferential direction of movement. Such manipulation involves the changing of the coordinate positions of the nodes. For example, the angular component of at least some of the polar coordinates of the nodes along the boundary may be modified in the same or opposite directions to produce an anti-torque effect. In another example, the height component and in some instances the radius component as well of the nodes along the boundary may be modified in the same or opposite directions to produce an anti-backout effect. In producing either of these effects, the struts may correspondingly be lengthened or shortened as necessary to maintain connectivity with the nodes along the boundary. The amount that any coordinate is changed can be based on any empirical or mathematical function.

A similar modification in the vertical direction is shown in FIG. 18. In this case the nodes on the outermost boundary of the porous CAD volume 500 are manipulated to be repositioned in the vertical direction to create features that are resistant to the part being extracted after insertion.

In another example, as illustrated in FIG. 21, surface features can be generated on any part where the surface is made up of connected nodes. Intrinsic surface properties can be created through the movement of nodes away from the surface to positions both inside and outside of the porous CAD volume. The location of the new position of a node 151-160 and corresponding struts 161-170 may be a parameter of the building application such that the repositioned node 151-160 will be at a position selected to satisfy a predetermined theoretical surface roughness along the predefined portion of the outer boundary 200. The theoretical surface roughness may be defined by a formula for surface roughness, such as any of the ANSI/ASME B46.1-2009 standards for surface roughness R_(a), R_(s), R_(z), or R_(q). In addition, the new positions of a group of nodes 151-160 and corresponding struts 161-170 along a predefined portion of the outer boundary 200 may be selected such that the surface roughness of the predefined portion of the outer boundary 200 is a predetermined value. Thus, the positions chosen may be selected at random so long as the aggregate of the positions of the nodes 151-160 and corresponding struts 161-170 satisfy the theoretical surface roughness chosen. For example, if R, is the parameter, then each of the struts 161-170 and nodes 151-160 along the outer boundary 200 must fall within a set distribution between minimum and maximum heights 275 and 285, respectively, as shown in FIG. 21.

FIGS. 23( a) and (b) depict the surfaces of flat structures formed using a conventional modeling method and some of the approaches described herein. FIG. 23( a) is a photograph of a coupon formed by selective laser melting of powdered metal prepared in accordance with a method known in the prior art. To produce the coupon, a model build structure was prepared with the upper nodes of the regular, octahedral, porous geometry deliberately intersecting the upper surface boundary of the cuboid porous CAD volume.

FIG. 23( b) is a photograph of another coupon formed using the same selective laser melting process as the coupon in FIG. 23( a). The model build structure used to produce the coupon in FIG. 23( b) used the same lattice structure as the coupon in FIG. 23( a). However, an approach in accordance with those described herein was employed to produce the top surface of the model build structure corresponding to the roughened top surface 200 shown in FIG. 23B. An algorithm was applied to the nodes at the upper surface of the porous CAD volume. This algorithm required a predetermined surface roughness (to a corresponding R_(a), S_(a) or other standard roughness measure) as described previously. FIG. 23( b) shows the resultant built geometry illustrating the surface roughness obtained.

The features previously described herein can be used on any surface. An example of their use on curved surfaces is shown in FIG. 22. A porous CAD volume that conforms to a surface 100 is used as the base. An upper bound 300 and lower bound 301 define a region 302 in which the surface nodes 25-35 can be repositioned. As in the example shown in FIGS. 8( a) and 8(b), the amplitude and direction of each movement can be controlled to create any predetermined theoretical surface quality e.g., roughness or surface marking. This same algorithm has been applied to a curved surface detailed in FIG. 24 where the nodes have been moved by a set amplitude to get a desired roughness value on a curved surface.

Specific use can be made of these different roughening algorithms to produce desired effects, for example surface marking for use in product identification. This can be seen in FIG. 25 which illustrates that it is possible to produce markings that are invisible under normal light, and visible under angular directed light, for example by creating areas of different roughness, which may be sub-flush or proud of the surface. This could also be applied in the form of a 2-D barcode or QR code that may contain proprietary information relating to the specific implant to which the coding has been applied. In this manner, the marking may be readable by hand-held laser scanners or other well-known devices.

Another application of the movement of the nodes along and through the surface is demonstrated in FIG. 26. These relate to the creation of an irregular appearance at the surface of a regular structure. The nodes that are at the surface can be moved along, out of, into or in any combination of these movements to create a modified surface that has irregular qualities but which is based on a regular structure.

Yet a further method of creating surface roughness is shown in FIG. 28. Additional struts 80 may be added onto the outer nodes 25-35 as defined in the arrangement shown in FIG. 12, and additional struts 520 may be added onto outer nodes 410-427 as defined in the arrangement of FIG. 16. These additional struts do not connect to another strut. In this manner, these struts may give rise to a resistance to movement in a direction at an angle sufficiently perpendicular to the surface.

As contemplated by an embodiment of this invention, self-retaining features, such as the additional struts 520, may be used to produce a “VELCRO” type effect in tangible structures formed from a corresponding model build structure. In this manner, the outside surface of one tangible structure having a self-retaining feature may be an inverse representation of the outside surface of a mating tangible structure having a corresponding self-retaining feature. For example, the mating structures may each have additional struts that interlock or engage with one another. In other embodiments, additional struts of one structure may fit into pores or holes on the surface of another structure in a “hook and eye” formation or through an interference fit to attach the two structures. As shown in FIGS. 33( a) and (b), elongated fixation elements 580 may be substantially parallel to each other and extend from the outer nodes 25-35. In the example shown, the fixation elements 580 are additional struts incorporated into the model build structure that are only connected to the model build structure at one end thereof in which the other end of each fixation element lies outside the boundary 100.

The fixation elements 580 may correspond to “microspikes” of an intended physical structure that are created using the model of the elements 580. The microspikes may mesh in an interference fit with another mating structure which may have receiving holes for the microspikes or which may be soft enough to permit the microspikes to puncture through a surface of the structure. For instance, the microspikes preferably may be capable of piercing through a bone surface, in particular a spongy bone surface. The elements 580 may extend in a predetermined direction relative to the boundary 100. When used in this manner, at least a portion of the fixation elements 580 preferably may be substantially parallel to each other such that the portion of the substantially parallel fixation elements has a density within a plane perpendicular to the fixation elements 580 of approximately 20 to 400 elements per square centimeter, and more preferably approximately 50 to 200 elements per square centimeter. Such densities may provide sufficient surface contact between the physical porous structure corresponding to the porous CAD volume and a mating structure in which the fixation elements may be inserted to maintain an interlock between the physical and mating structures. When a portion of the fixation elements 580 are substantially parallel to each other, the fixation elements 580 also may preferably be spaced a distance from each other that is larger than the largest pore diameter of the bone.

The fixation elements 580 may extend in a number of predetermined directions relative to the boundary. In some arrangements, the fixation elements 580 may be perpendicular to the boundary 100. As shown in the example of FIGS. 33( a) and (b), the elements 580 may extend, in some instances, in a direction that is different from the direction of struts 581 that intersect with struts forming the boundary of the porous CAD volume. The fixation elements 580 preferably may form an angle of 10° to 90°, and more preferably may form an angle of 30° to 90°, with the boundary 100. Typically, the predetermined direction of fixation elements 580 intended to be mated with a structure will be substantially parallel to the direction of a seating area of a mating structure into which the fixation elements 580 are adapted to be received.

In accordance with another embodiment, with specific reference to FIGS. 34( a) and (b), adjacent struts 685, 686 may be attached to the porous CAD volume, extending from the outer nodes 25-35 on one end and be attached to each other on the other end at nodes 1027-1035 to form portions of a plurality of elongated fixation elements 690. For example, strut 685 may extend from node 335 on one end to node 1035 on the other end. Likewise, strut 686 may extend from node 34 on one end to node 1035 on the other end. Similarly, other adjacent struts 685, 686 along the boundary 100 may extend from the porous CAD volume and connect to each other.

It should be noted that FIGS. 33( a) and (b) and FIGS. 34( a) and (b) only illustrate a two-dimensional slice of a portion of the porous CAD volume. Accordingly, in the example of FIG. 34, two or more other struts (not shown) may be connected to both strut 685 and strut 686 to form other sides of a fully connected porous geometry (e.g., formed using a tetrahedron unit cell as described previously herein) that form the elongated fixation element 690. The fixation element 690 may be more space-filling, but may also provide greater bending and torsional strength than the fixation elements 580 shown in FIG. 33. These space-filling fixation elements may also provide for interference fits with mating structures. Due to their greater surface area for contacting a mating structure, these fixation elements may also provide for greater adhesion to a mating structure than fixation elements, such as elongated fixation elements 580.

As in the example shown in FIGS. 34( a) and (b), the fixation elements 690 may have a longitudinal axis extending between each of the connected struts extending from the porous CAD volume. Moreover, as in the arrangement shown, the longitudinal axes of the fixation elements 690 may be substantially parallel to each other along at least a portion of the boundary 100. In such a configuration, the fixation elements 690 preferably may have a density within a plane perpendicular to the longitudinal axes through the fixation elements 690 of approximately 20 to 500 elements per square centimeter, and more preferably approximately 50 to 300 elements per square centimeter.

In the views shown in FIGS. 35( a)-(c), elongated fixation elements 790 are formed by struts 785 and 786 and two other struts (not shown) in a manner similar to that described for the fixation elements 690. In contrast with the fixation elements 690, however, the fixation elements 790 extend from a solid CAD volume 795. In this manner, the fixation elements 790 extend from nodes 791 formed at the interface of the solid CAD volume 795 and a porous CAD volume 780. Moreover, in the arrangement shown, fixation elements 790 are formed such that a longitudinal axis through the fixation elements is perpendicular to a plane tangential to the solid CAD volume 795 at an imaginary point of intersection between the longitudinal axis and the solid CAD volume 795. Accordingly, when used in the tapered cylindrical geometry shown in the views of FIGS. 35( a) through (c), the elongated fixation elements 790 extend from the solid CAD volume 795 such that the longitudinal axes of fixation elements 790 within a given plane around the circumference of the model build structure are not parallel.

As shown in FIG. 36, a model build structure of a femoral knee implant 1100 may be formed in the manner described previously herein such that a porous CAD volume 1180 is mated to a solid CAD volume 1195 at an interface 1185. As shown, elongated fixation elements, such as the fixation elements 1191, 1192 may extend from the porous CAD volume 1180 such that the longitudinal axes through at least some of the elongated fixation elements is not parallel. In this manner, the fixation elements may be used to create microspikes of the intended implant that correspond to the fixation elements which resist movement of the implant in multiple directions to secure the implant against a patient's femur. In alternative arrangements, the fixation elements may extend from the solid CAD volume 1195 at the interface 1185 in a manner similar to the extension of the fixation elements 790 shown in FIGS. 35( a)-(c). In the example of FIG. 36, the fixation elements may be portions of fully connected porous geometries, such as those shown in FIGS. 34( a) and (b) and FIGS. 35( a)-(c), although other shapes of fixation elements may be used such as single struts, like those shown in FIG. 33.

As is shown by the portion of a model build structure used for a tray of a tibial knee implant 1200 in FIGS. 37( a) and (b), fixation elements 1290 may be formed to extend from a solid geometry 1295. In this manner, when an intended physical structure is formed using a rapid prototyping process as described further herein, the fixation elements 790 may be built, such as through powder metal processes, directly onto a substrate. Furthermore, the fixation elements 1290 may additionally be formed such that they extend through a porous CAD geometry 1280. In this manner, a porous ingrowth structure (corresponding to and built using the porous CAD geometry 1280) may provide structural support along a portion of microspikes (corresponding to and built using the fixation elements 1290) during sideloading against the microspikes.

Still other formations along the surface of the porous CAD volume include a barbed geometry with corresponding ends, a hooked geometry with corresponding ends, deformable loops, or variations in the depth of the roughening applied to mating surfaces as described previously herein, to create an interlock between the mating surfaces. In some instances, these types of positive engagement may remove or minimize the need for mechanical fixation devices such as bone screws or other assembly devices.

Other variations of the fixation elements and corresponding microspikes also may be used. The microspikes may be formed using other shapes of unit cells, e.g., octahedral, dodecahedral, etc. The fixation elements and corresponding microspikes may have various shapes and sizes in comparison to other structures having these features. Moreover, various shapes and sizes of fixation elements and microspikes may be used at different portions of the surface of a corresponding CAD geometry or corresponding intended physical structure, respectively. Furthermore, the microspikes and corresponding fixation elements may or may not be used in conjunction with additional engineering structures and respective models thereof, such as keels, pegs, stems, and spikes, for additional device stabilization. Such engineering structures may be integral, i.e., form part of a monolithic structure, with or may be separately added or fixed to, e.g., by fasteners, to intended physical structures. When used in conjunction with additional engineering structures, the fixation elements and corresponding microspikes may extend from the additional engineering structures themselves as well as from other portions of the respective model build structure and intended physical structure. Although the formation and use of fixation elements (and corresponding microspikes) have been described with respect to a femoral and tibial knee implants, such features may be used in the production of other prosthetic devices such as acetabular, patella, shoulder glenoid, finger, and ankle implants, or the like.

A flow diagram shown in FIG. 29 details an embodiment of the creation of porous geometries within a Cartesian coordinate defined unit cell. At block 610, a computer-generated model of a three-dimensional structure is prepared. A bounding box is created by a processor. This bounding box is populated with unit cells 620.

The spatial interaction of the unit cells with the surface of the porous CAD volume is determined, by a processor, and two pathways are created at a step 630. The unit cells that do not make contact with the surface are then interrogated to determine their position at a step 640. Unit cells that lie outside the structure are discarded. Unit cells that are within the porous CAD volume are populated with porous geometries 650.

The unit cells that cross the surface of the porous CAD volume are populated with porous geometries. The struts of porous geometries can then either be clipped to the surface at a step 670 or clipped to a node at a step 680 as described previously herein. In other words, the struts may be clipped to an inner node, an outer node, or at the boundary of the porous CAD volume. However, this approach may leave the surface rough, uneven, and nonconforming to the original porous CAD volume.

Through steps 690-692, the nodes at the surface can also be manipulated so that all the surface nodes lie on the outer boundary of the porous CAD volume to create a conformal surface.

A process flow diagram shown in FIG. 30 details an embodiment of the creation of porous geometries within polar or cylindrical coordinate defined unit cells. At a step 710, a computer-generated model of a three-dimensional structure is prepared or a part is defined using geometric parameters.

This model may then be sliced virtually at a step 720 to produce polar rings that can then be populated with unit cells and nodes in a radial pattern at a step 730. These unit cells may be populated with porous geometries at a step 740.

A process flow diagram shown in FIG. 31 details an embodiment the creation of surface features through repositioning of nodes that lie on the boundary of the porous CAD volume. This operation can be performed on any porous geometry that consists of struts which interconnect at nodes along the boundary of the porous CAD volume.

At least one node is selected at a step 810 which can then be perturbed in a variety of ways to generate the desired surface properties. In one embodiment, a node along the boundary can be repositioned along a position vector which is at an angle to the surface direction as shown at steps 830-831. This process may be used to create surface properties such as surface roughness.

In another embodiment, a node can be moved along a position vector parallel to the surface direction across the surface which can be used to create torque or movement resisting, pullout resisting and surface irregularity properties at steps 840 and 841.

In yet another embodiment, any combination of the steps 830 and 840 may be used to create surface properties. Nodes can be moved both along and away from the surface to create areas of irregularity, roughness and marking at steps 850 and 851.

In another example as shown in FIG. 32, a computer-generated component file is prepared at a block 910. The component file includes a porous CAD volume with a boundary having at least one predefined portion. At a block 920, a space that includes the porous CAD volume is populated, by a processor, with unit cells that overlap the predefined portion of the boundary. Such a space may be defined by sets of coordinates, such as Cartesian, polar, or spherical coordinates. At a block 930, the unit cells are populated with porous geometries. Within the porous geometries may be a plurality of struts. At least one end of the struts may have a node. As further shown at block 930, at least one of the struts overlaps the predefined portion of the boundary. Such a strut has a length, one node outside the porous CAD volume, and one node inside the porous CAD volume. At block 940, any struts entirely outside the predefined portion of the boundary are removed. In some embodiments, any struts outside the entire boundary are removed. In this manner, a computer-generated model of a three-dimensional structure constructed of porous geometries is prepared. At an optional block 950, a tangible three-dimensional structure having a shape corresponding to the computer-generated model may be produced. The shape of the three-dimensional structure may be in the form of a geometric lattice structure.

Visualization of all of the above effects under consideration can be achieved by voxelating the sliced output files from bespoke software that is being applied in an additive layer manufacturing machine. Utilizing developed algorithms and the output files, the data may be fed into a commercial software package, e.g., Matlab, and the images produced can be interpreted. FIGS. 2( a) and 2(b) illustrate an initial process operation in contrast to FIGS. 19, 20 and 26 representing common output images.

The approaches for generating three-dimensional models described herein may be used for building various tangible structures and surfaces, specifically structures and surfaces for medical implants. Although a brief summary follows, many details of the process of melting powdered metal are given in the '421 and '327 Applications. In constructing a tangible structure from a model build structure, a layer of metal powder, in some instances, may be deposited on a substrate. The substrate may be a work platform, a solid base, or a core, with the base or core being provided to possibly be an integral part of the finished product.

The metal powder may be Ti alloys, stainless steel, cobalt chrome alloys, Ta or Nb. In some embodiments, individual layers of metal may be scanned using a directed high energy beam, such as a laser or e-beam system to selectively melt the powder, i.e., melt the powder in predetermined locations. Each layer, or portion of a layer, is scanned to create a plurality of predetermined porous geometries by point exposure to the energised beam. This leads to the production of struts that correspond to the struts described previously herein, as will be described below. Successive layers are deposited onto previous layers and also are scanned. The scanning and depositing of successive layers continues the building process of the predetermined porous geometries and oblique struts are directed to nodes. As disclosed herein, continuing the building process refers not only to a continuation of a porous geometry from a previous layer but also a beginning of a new porous geometry as well as the completion of the current porous geometry.

In a preferred aspect of the present invention, the high energy beam may be adjusted to modify the cross-sectional diameter of various struts. Some of the struts of the porous geometries may overlap struts of other porous geometries as a result of randomization within unit cells, but such struts never lose their identity with respect to their origin. Dimensions of strut diameter and unit cell size may enable the adjusting of the porosity throughout the completed structure. The strut diameter preferably should be nominally two times the diameter of the high energy beam, and each unit cell should have sides with lengths preferably no greater than 2 mm and have an aspect ratio that is limited to a maximum of 1:2 with respect to a maximum height of the unit cell.

In some embodiments, a component structure or sub-structure thereof produced by the approaches herein may be porous and if desired, the pores can be interconnecting to provide an interconnected porosity. In some embodiments, the amount and location of porosity may be predetermined, and preferably lie in the range 50% to 90% as being suitable when used as a bone ingrowth surface, and 20% to 90% as being suitable for polymer interlock surfaces. This also applies to cases where the outer porous section of a medical device is connected to host bone with bone cement or bone type adhesives for example. A base or core of cobalt chrome alloy, titanium or alloy thereof, stainless steel, niobium and tantalum, may be used to build a porous layer of any one of these metals and/or alloys by melting using high energy beam, such as a continuous or pulsed laser beam or an electron beam. Thus, a mixture of desired mixed materials can be employed. The porous layers can be applied to an existing article made from cobalt chrome, titanium or alloy, stainless steel, tantalum or niobium, such as an orthopaedic implant. It is thus intended that the approaches described herein may be exploited to produce commercially saleable implants with bone in-growth structures having porous surfaces with a controllable texture or surface profile. Such an implant may be an acetabular component, a knee tibial or patella implant, a femoral knee or hip implant, or the like. The constructed medical implant may have a porosity and architecture optimised, to create very favourable conditions so that bone in-growth takes place in a physiological environment and the overall outcome favours long-term stability.

The medical implants, as well as other constructed structures, may be provided with an attaching mechanism for anchoring or at least more firmly attaching the medical implant to another element. One such example is an acetabular component being provided with a surface structure which mates with the surface of an augment component.

Because a laser melting process may not require subsequent heat treatment or the temperature at which this heat treatment occurs is lower than any critical phase change in the material, the initial mechanical properties of any base metal to which a porous structure is applied may be preserved.

The equipment used for the manufacture of such a device could be one of many currently available including but not limited to those manufactured by Renishaw, SLM Solutions, Realizer, EOS, Concept Laser, Arcam and the like. The laser or electron beam may also be a custom produced laboratory device.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. 

The invention claimed is:
 1. A method of preparing a computer-generated model of a three-dimensional structure constructed of porous geometries, the method comprising: preparing a computer-generated component file including a porous CAD volume having a boundary; populating, by a processor, a space including the porous CAD volume with unit cells, at least one unit cell overlapping the boundary; populating, by a processor, the unit cells with porous geometries, a plurality of the porous geometries having a plurality of struts having opposing ends, each end being connected at a corresponding node, at least one strut overlapping the boundary and having a length, a first node outside the porous CAD volume, and a second node inside the porous CAD volume; removing, by a processor, all struts entirely outside the porous CAD volume such that each end of the remaining struts remains connected at its corresponding node; and populating, by a processor, the space with at least one elongated fixation element extending beyond the boundary to produce an interlocking feature to enable assembly or engagement with a mating structure.
 2. The method of claim 1, wherein at least a first strut intersects a second strut at a node, and wherein the at least one elongated fixation element intersects the node at which the first strut intersects the second strut.
 3. The method of claim 2, wherein the at least one elongated fixation element extends in a predetermined direction relative to the boundary.
 4. The method of claim 1, wherein the at least one elongated fixation element extends in a predetermined direction relative to the boundary.
 5. The method of claim 4, wherein the at least one elongated fixation element is a plurality of elongated fixation elements extending beyond the boundary in a direction perpendicular to the boundary, each of the plurality of elongated fixation elements defining corresponding longitudinal axes therethrough, wherein the plurality of elongated fixation elements are substantially parallel, and wherein the intersections of the longitudinal axes of the fixation elements and the boundary have a density lower than the porosity of the mating structure.
 6. The method of claim 1, wherein the at least one elongated fixation element intersects the boundary.
 7. The method of claim 1, wherein the component file further includes a solid volume contacting the porous CAD volume, and wherein the at least one elongated fixation element extends from the solid volume through the porous CAD volume.
 8. The method of claim 1, wherein at least first and second elongated fixation elements populated by the processor extend beyond the boundary, and wherein the first and second elongated fixation elements are substantially parallel.
 9. The method of claim 1, wherein at least first and second elongated fixation elements populated by the processor extend beyond the boundary, and wherein the first and second elongated fixation elements are substantially nonparallel.
 10. The method of claim 1, wherein the at least one elongated fixation element has a cross-section along a length thereof that is one of substantially (i) cylindrical, (ii) rectangular, (iii) triangular, (iv) hexagonal, and (v) octagonal.
 11. The method of claim 1, wherein the at least one elongated fixation element is tapered along a length thereof.
 12. The method of claim 1, wherein the at least one elongated fixation element has a helical exterior along a length thereof.
 13. A method of producing the three-dimensional structure comprising: preparing the computer-generated model of the three-dimensional structure according to claim 1; depositing a metal powder onto a substrate; scanning a beam onto the deposited metal powder to form a first physical layer of a porous section corresponding to a portion of the porous CAD volume of the model of the three-dimensional structure, the three-dimensional structure having a geometric lattice structure constructed of porous geometries and a boundary, the porous geometries formed by a plurality of struts, each of the plurality of struts having a node on each end thereof, repeating the step of depositing the metal powder onto the substrate; repeating the step of scanning the beam onto the deposited metal powder to form additional physical layers of the three-dimensional structure; and forming at least one elongated fixation member for assembly or engagement with a mating structure, the at least one elongated fixation member corresponding to the at least one elongated fixation element and extending beyond the boundary.
 14. The method of producing the three-dimensional structure according to claim 13, wherein the beam is at least one of (i) an electron beam and (ii) a laser beam.
 15. The method of claim 13, wherein the step of forming the at least one elongated fixation member comprises the steps of: depositing a metal powder onto one of the (i) substrate and (ii) porous section; scanning a beam onto the deposited metal powder to form a first physical layer of the at least one elongated fixation member; repeating the step of depositing the metal powder onto the one of the (i) substrate and (ii) porous section; repeating the step of scanning the beam onto the deposited metal powder to form additional physical layers of the at least one elongated fixation member.
 16. The method of claim 13, wherein at least first and second elongated fixation elements populated by the processor extend beyond the boundary in a direction perpendicular to the boundary, and wherein the first and second elongated fixation elements are substantially parallel, wherein at least first and second elongated fixation members for assembly or engagement with a mating structure are formed, and wherein the first and second elongated fixation members are substantially parallel.
 17. The method of claim 13, wherein at least first and second elongated fixation elements populated by the processor extend beyond the boundary in a direction perpendicular to the boundary, wherein the first and second elongated fixation elements are substantially nonparallel; and forming at least first and second elongated fixation members for assembly or engagement with a mating structure are formed, and wherein the first and second elongated fixation members are substantially nonparallel.
 18. The method of claim 17, wherein the porous section is a porous bone-ingrowth structure of a femoral knee implant having at least an anterior surface and an anterolateral chamfer surface adjacent thereto, wherein the first elongated fixation element extends from the anterior surface, and wherein the second elongated fixation element extends from the anterolateral chamfer surface.
 19. The method of claim 1, further comprising removing the first strut when the first node is further from the boundary than the second node.
 20. The method of claim 19, the second node being further attached to at least one adjacent strut inside the porous CAD volume, further comprising: moving a closer of the first and the second nodes to the predefined portion of the boundary at a position along the predefined portion of the boundary; and when the first node is the closer node, changing the length of at least the first strut such that the first strut remains connected to the first node, and when the second node is the closer node, changing the length of the at least one adjacent strut such that the at least one adjacent strut remains connected to the second node.
 21. A non-transitory computer-readable storage medium on which computer readable instructions of a program are stored, the instructions, when executed by a processor, cause the processor to perform a method of preparing a computer-generated model of a three-dimensional structure constructed of unit cells, the method comprising: preparing a computer-generated component file including a porous CAD volume having a boundary; populating, by a processor, a space including the porous CAD volume with unit cells, at least one unit cell overlapping the boundary; populating, by a processor, the unit cells with porous geometries, a plurality of the porous geometries having a plurality of struts having opposing ends, each end being connected at a corresponding node, at least one strut overlapping the boundary and having a length, a first node outside the porous CAD volume, and a second node inside the porous CAD volume; removing, by a processor, all struts entirely outside the porous CAD volume such that each end of the remaining struts remains connected at its corresponding node; and populating, by a processor, the space with at least one elongated fixation element extending beyond the boundary to produce an interlocking feature to enable assembly or engagement with a mating structure. 